Optical scanning devices of this type are used, for example, in CD players in order to be able to read by means of a light beam the data of an optical compact disc, a so-called CD.
An objective lens by means of which a light beam is focused onto the disk, is seated on a lens holder supported rotatably about an axle so that the objective lens is movable in the radial direction with respect to the disk. The lens holder is fastened rotatably on a housing which is movable in the radial direction with respect to the disk. It is known, for example, to place the housing on a spindle so that by rotating the spindle it can be moved in the radial direction over the data tracks of the disk. This mechanism, most often referred to as coarse drive, serves for the purpose of being able to position the objective lens over any desired data track of the disk. Because of the rotational motion of the lens holder, already described, relative to the housing the objective lens can be positioned more precisely or more finely over the data tracks. This is therefore referred to as a so-called fine drive.
The vertical motion along the optical axis of the objective lens and the rotational motion of the lens holder are brought about by means of coils which are disposed either on the housing, on the lens holder or on both parts. Most frequently magnets are provided as counter parts to the coils in order to generate a magnetic force between the coils and the magnets.
Several demands are made simultaneously of optical scanning devices of this type: so that low magnetic forces already effect a lifting and a rotational motion of the objective lens, the lens holder should be of low mass and should be readily rotatable as well as readily movable in the up and down direction.
If the coils are seated on the movable lens holder, electrical wires must be provided as feed lines. But these wires increase not only the weight of the lens holder, they also increase the mechanical resistance against the rotational and lifting motions of the lens holder because they limit its movability. Lastly, it should be possible to produce the optical scanning device cost-effectively in series.
It is therefore the task of the invention to implement an optical scanning device with a lens holder which is rotatable about an axle and at whose one end is seated a lens in such a way that it can be produced cost-effectively and so that its lens holder is distinguished by low mass and low mechanical friction.